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__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
___ __ __ _ ___
/ | /_\ /
\___ __|__ / \ \___
__________________________________________________________
INFORMATION BULLETIN
rdist vulnerability
July 24, 1996 17:00 GMT Number G-33
______________________________________________________________________________
PROBLEM: A new vulnerability has been discovered in the rdist program,
and an exploit script is being widely distributed for this
vulnerability.
PLATFORM: Any UNIX system with an unpatched rdist that is set-uid to root.
DAMAGE: This vulnerability can allow an unprivileged local user to gain
root access.
SOLUTION: Apply the patches listed in the Vendor section of the bulletin
below.
______________________________________________________________________________
VULNERABILITY This vulnerability is widely known, and exploit scripts are
ASSESSMENT: being distributed over the Internet. It is highly recommended
that you apply these patches as soon as possible.
______________________________________________________________________________
[ Begin CERT Bulletin ]
=============================================================================
CERT(sm) Advisory CA-96.14
July 24, 1996
Topic: Vulnerability in rdist
This advisory supersedes CA-91:20.rdist.vulnerability and
CA-94:04.SunOS.rdist.vulnerability.
- - -----------------------------------------------------------------------------
The CERT Coordination Center has received reports that a new vulnerability
in rdist has been found and an exploitation script is widely available.
Current reports indicate that the script works on x86-based versions of the
UNIX Operating System; however, we believe that it would not be difficult to
write variants that work on other instruction sets and configurations.
The CERT/CC Staff recommends following the steps in Section III.A. to
determine if your system is vulnerable and to disable vulnerable programs,
then following your vendor's instructions (Section III.B and Appendix A).
Until you can install a vendor patch, you may want to install a freely
available version of rdist, noted in Section III.C.
As we receive additional information relating to this advisory, we
will place it in
ftp://info.cert.org/pub/cert_advisories/CA-96.14.README
We encourage you to check our README files regularly for updates on
advisories that relate to your site.
- - -----------------------------------------------------------------------------
I. Description
The rdist program is a UNIX Operating System utility used to distribute
files from one host to another. On most systems, rdist is installed as
set-user-id root, a necessity due to its design. Unfortunately, this
setting makes it a favorite target for vulnerability investigation.
A new vulnerability in rdist has been discovered and reported. The
vulnerability lies in the lookup() subroutine where the value of a
command line argument is used to overflow the subroutine call stack.
If that argument is specially crafted with native machine code,
lookup() returns control to the code added to the call stack instead of
the subroutine that called lookup(). If, for example, this added code
uses a member of the exec system call family and names /bin/sh as the
program to be executed, that shell is then run with set-user-id root
privileges. No matter what code is added, the code runs with
set-user-id root privileges.
An exploitation program, which is circulating on the Internet, takes
advantage of this vulnerability. While it purports to work only on
x86-based versions of the UNIX Operating System, variants tuned to other
instruction sets and configurations are straightforward to write.
II. Impact
On unpatched systems, anyone with access to a local account can gain root
access.
III. Solution
We urge you to follow the steps in Section A to determine if your system
is potentially vulnerable and, if it is, to turn off rdist while you
decide how to proceed.
If you need the functionality that rdist provides, install a vendor
patch (Sec. B). Until you can do so, you may want to install a freely
available version of rdist that does not need to be installed as
set-user-id root and is, therefore, not susceptible to the exploitation
described in this advisory (Sec. C).
A. How to determine if your system is vulnerable
To determine if a system is vulnerable and to disable the programs
that are believed to be vulnerable, use the following find command or
a variant. Consult your local system documentation to determine how to
tailor the find program on your system.
You will need to run the find command on each system you maintain
because the command examines files on the local disk only. Substitute
the names of your local file systems for FILE_SYSTEM_NAMES in the
example. Example local file system names are /, /usr, and /var.
You must do this as root.
Note that this is one long command, though we have separated
it onto two lines using a back-slash.
find FILE_SYSTEM_NAMES -xdev -type f -user root \
-name rdist -perm -04000 -print -ok chmod u-s '{}' \;
This command will find all files on a system that are
- only in the file system you name (FILE_SYSTEM_NAMES -xdev)
- regular files (-type f)
- owned by root (-user root)
- named rdist
- setuid root (-perm -04000)
Once found, those files will
- have their names printed (-print)
- have the setuid mode removed, but only if you type `y'
in response to the prompt (-ok chown u-s '{}' \;)
B. Obtain and install the appropriate patch
Below is a list of the vendors who have reported to us as of
the date of this advisory. Details are in Appendix A.
Berkeley Software Design, Inc.
Data General Corporation
FreeBSD, Inc.
Hewlett-Packard Company
IBM Corporation
Linux
NEC Corporation
The Santa Cruz Operation
Sequent Computer Systems
Silicon Graphics, Inc.
Sun Microsystems, Inc.
If your vendor's name is not on this list, please contact the vendor
directly.
Appendix A is reproduced in CA-96.14.README, which will be updated as
we receive additional information.
C. If you need the functionality that rdist provides but a patched
version is not yet available from your vendor, consider installing
rdist-6.1.3, which is freely available from
ftp://usc.edu/pub/rdist/rdist-6.1.3.tar.gz
MD5 (rdist-6.1.3.tar.gz) = 8a76b880b023c5e648b7cb77b9608b9f
The README file in the distribution explains how to configure
and install this version of rdist.
We strongly recommend that you configure this version of rdist to use
rsh instead of rcmd. Here is the relevant text from the README:
By default rdist uses rsh(1c) to make connections to remote
hosts. This has the advantage that rdist does not need to be
setuid to "root". This eliminates most potential security
holes. It has the disadvantage that it takes slightly more time
for rdist to connect to a remote host due to the added overhead
of doing a fork() and then running the rsh(1c) command.
For versions of rdist V6 prior to 6.1.3: If you compile rdist with
-DDIRECT_RCMD *and* you run rdist setuid to root, you are vulnerable
to the problem described in this advisory. You need to update to
rdist version 6.1.3.
Note that by default, rdist V6 is distributed to compile without
-DDIRECT_RCMD and not run setuid to root. If you have previously
built version 6.X of rdist with the -DDIRECT_RCMD directive added to
the $(DEFS_LOCAL) and set "RDIST_MODE = 4555" in "Makefile.local", we
recommend that you first disable this version with the find command
given in Section III.A above, then either rebuild rdist with its
default settings or upgrade to 6.1.3.
- - ---------------------------------------------------------------------------
The CERT Coordination Center staff thanks Michael Cooper
(Michael.Cooper@Sun.Com) for his work on resolving this problem. He is the
maintainer of the publicly available version of rdist.
- - ---------------------------------------------------------------------------
Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.
CERT is a service mark of Carnegie Mellon University.
This file: ftp://info.cert.org/pub/cert_advisories/CA-96.14.rdist_vul
http://www.cert.org
click on "CERT Advisories"
.........................................................................
Appendix A: Vendor Information
Current as of July 24, 1996
See CA-96.14.README for updated information.
Below is information we have received from vendors concerning the
vulnerability described in this advisory. If you do not see your vendor's
name, please contact the vendor directly for information.
Berkeley Software Design, Inc.
==============================
BSD/OS is vulnerable to this problem.
BSDI has released a patch for rdist in BSD/OS V2.1.
Sites using the non-kerberized rdist should install patch
U210-018, which is available from the patches@bsdi.com
mailback server and also from:
ftp://ftp.bsdi.com/bsdi/patches/patches-2.1/U210-018
md5 checksum: 86005d8bbb67eb737120741bd254d26a U210-018
Domestic licensees that are using the Kerberos package
should install patch D210-018 from the patches@bsdi.com
mailback server (this patch is available only to domestic
licensees because of US export restrictions on crypto
software). Be sure to install only the appropriate patch.
md5 checksum: b2060ec4eb9b18ace4e76bcb9441353f D210-018
Data General Corporation
========================
Data General does not provide a version of rdist as part of the
standard release of DG/UX. Rdist is available as contributed
software which is not supported by Data General. This problem will
be fixed in the next release of the contributed software package.
FreeBSD, Inc.
=============
Versions affected:
FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
Versions corrected:
2.1-stable and 2.2-current as of 1996-07-11
Workaround:
As root, execute the commands:
# chflags noschg /usr/bin/rdist
# chmod u-s,go-rx /usr/bin/rdist
Patches:
ftp://freebsd.org/pub/CERT/patches/SA-96:16/
For more information:
ftp://freebsd.org/pub/CERT/advisories/SA-96:16/
Hewlett-Packard Company
=======================
HP/UX 10.X is vulnerable, 9.X is not vulnerable.
Patches are in process.
IBM Corporation
===============
AIX is vulnerable to this problem. Fixes are in process but are
not yet available. The APAR numbers for the fixes are given below.
In the meantime, we recommend removing the setuid bit from the
/usr/bin/rdist program.
To remove the setuid bit, follow these instructions.
As the root user, type:
chmod u-s /usr/bin/rdist
AIX 3.2
-------
Apply the following fix to your system:
APAR - IX59741
AIX 4.1
-------
Apply the following fix to your system:
APAR - IX59742
To determine if you have this APAR on your system, run the following
command:
instfix -ik IX59742
AIX 4.2
-------
Apply the following fix to your system:
APAR - IX59743
To determine if you have this APAR on your system, run the following
command:
instfix -ik IX59743
To Order
--------
APARs may be ordered using FixDist or from the IBM Support Center.
For more information on FixDist, reference URL:
http://aix.boulder.ibm.com/pbin-usa/fixdist.pl/
or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".
IBM and AIX are registered trademarks of International Business Machines
Corporation.
Linux
=====
Almost all Linux distributions ship with rdist non setuid.
If you have changed your rdist to run setuid you are probably
vulnerable.
NEC Corporation
===============
EWS-UX/V(Rel4.2) not vulnerable
EWS-UX/V(Rel4.2MP) not vulnerable
UP-UX/V(Rel4.2MP) not vulnerable
UX/4800 not vulnerable
The Santa Cruz Operation
========================
The following releases of SCO Software are known to contain a version of
rdist that is vulnerable:
SCO OpenServer 5.0.2, 5.0.0
SCO Internet FastStart 1.0
SCO Open Server Enterprise/Network System 2.0, 3.0
SCO Open Desktop 2.0, 3.0
SCO Open Desktop Lite 3.0
SCO UnixWare 2.0, 2.1
SCO TCP/IP 1.2.0, 1.2.1
Patches are being developed for the following releases:
SCO OpenServer 5.0.2, 5.0.0
SCO Internet FastStart 1.0
SCO UnixWare 2.1
Sequent Computer Systems
========================
Sequent systems do not ship with rdist.
Silicon Graphics, Inc.
======================
All SGI IRIX versions of rdist are not vulnerable.
No action is required.
Sun Microsystems, Inc.
======================
The following patches correct the rdist vulnerability (Sun bug id 1258139),
described in this advisory, on systems running Solaris 1.x or 2.x.
Architecture SunOS Solaris Patch MD5 checksum for rdist binary
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SPARC 4.1.3 1.1 100383-07 5F2C2B782881FE18D2737B5FA0AEC489
4.1.3_U1 1.1.1 103823-01 B330358F4E66CD544B9B60AF453C5F2B
4.1.4 1.1.2 103824-01 11BDEC384048CD42200BC1D0F25B61C9
5.3 2.3 101494-02 1DD34E9E7C50B2C863E30D67DFD1A905
5.4 2.4 103813-01 90DD81A4C32F7D583737F171B821386B
5.5 2.5 103815-01 C3BBE3F6758B0BBA7D45CB05009ED80E
5.5.1 2.5.1 103817-01 89735351119896FEB7469DCA76788561
X86 5.4 2.4 103814-01 EE4509D9CF87DBD29ABB7A72C8330F89
5.5 2.5 103816-01 3363670F316A06803ECCDD9FFAE95126
5.5.1 2.5.1 103818-01 8C2E8CFDE7A2AE6D5EC89139D592E71C
PowerPC 5.5.1 2.5.1 103819-01 C3FC0E54B23E4209496A4735D09DFFEF
These patches will be available through your local SunService and SunSoft
Support Services organizations by 9:00 PDT Wednesday, July 24. They will
also be available at the same time from SunSolve Online, via the URL
http://sunsolve1.sun.com.
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of CERT for the
information contained in this bulletin.
_______________________________________________________________________________
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